Extending ring main and lighting in to new extension

[If in doubt...]

Hi, I'd appreciate some advice.

Sketch shows new single storey extension being built. Red stars are existing double sockets on ring main fed by fairy recent new CU with 32A MCB. Whilst I'm confident in running T&E and sockets etc I'm no qualified electrician but I would much prefer to do the work myself if possible. Not so much for cost but having half built most of the extension myself and also the flexibility of installing / tweaking as I go. Green stars are rough idea of possible new sockets but not firmed up yet. A couple of ceiling lights will also be run from existing lighting circuit.

Extension being built under building notice and my understanding is these electrical works are not notifiable? But is it simple case that BC will just acknowledge this or will they expect to see / review anything else? For peace of mind I will probably get someone in to test everything anyway at some point - but I'd like to get 1st fix underway shortly. Ta.

 

[Taylortwocities]

Depends on where you live. In England, extending an existing circuit is not notifiable.
Different rules are in place for some of the colonies.
Although the work is not notifiable, LABC will expect it to conform to Part P and, therefore, BS7671.

 

[ericmark]

I found LABC inspector wanted to control all aspects of building work even if not technically required to be inspected by them, this in my case included fitting extractor fans even when not required. So I would check with the LABC inspector first, as no one can sign the installation certificate other than the people doing the work.

So theory is a B32 MCB/RCBO needs between 3 and 5 times 32 amp to trip the magnetic part of the trip, and to ensure the magnetic part will operate with a short circuit one also allows 5% safety margin. So it needs 168 amps to flow, ohms law 230/168 = 1.37 Ω. The cheap plug in testers will normally pass at around 1.9 Ω so that means you need the full blown loop impedance tester which cost around £200, also a RCD tester, and insulation resistance tester, without them you can't complete the installation certificate.

The normal way is to get an EICR done after, and this will give you all the readings, but the problem is what will the LABC inspector accept? Often they want an electrician they select to do the tests, and this can work out more expensive than getting a scheme member to do all the work for you and the scheme provider issues the compliance certificate.

In theory anyone with the knowledge can issue the EIC or EICR, they do not need to be scheme members or issue the certificate under the scheme, but in practice it is down to who the LABC will trust, the EICR can be underwritten by the scheme provider, they use a different colour for one issued with or without the scheme providers authorization, and the electrician has to pay extra to have the EICR underwritten by the scheme provider, so in most cases they are not.

So down to your LABC inspector, and what he wants, and no one can say what he will want, other than him.

 

[FrodoOne]

Extending a "Ring" ?
Why ?

Use multiple "Radials"
Much easier and more convenient, with the increased possibility of ease of locating any future faults.

 

[SUNRAY]

Extending a "Ring" ?
Why ?

Use multiple "Radials"
Much easier and more convenient, with the increased possibility of ease of locating any future faults.

I still don't understand such comments.
How is installing larger CU's with more OCPD's and lots of runs of cable more convenient or easier? Why all the extra cost and bulk of additional OCPD's and cable?

I'll agree faults show quicker with radials and possibly easier to find. However experienced/competent personal don't generally have problems, on that basis should we really be moving away ring finals to make it easier for amateurs?

 

[Taylortwocities]

Extending a "Ring" ?
Why ?

Use multiple "Radials"
Much easier and more convenient, with the increased possibility of ease of locating any future faults.

Big thing.
New circuit means notification to LABC.
Extending existing is not notifiable.

In a perfect World then a radial circuit would be the ideal solution.
But most of us don’t live there.

 

[ericmark]

I still don't understand such comments.

He does not live in the UK, and likely does not realise the problems with Part P.

But to be within the volt drop on a ring final the amount of 2.5 mm² cable is considered as being limited to around 106 meters, with a radial assuming 20 amp that's down to 32 meters, so one needs three radials to replace one ring final.

Where radials fall over is items with a high in rush, I have seen where 110 volt yellow bricks will not work with a radial as the in rush exceed the 100 amp of a B20 MCB magnetic trip limit.

To be frank no one seems to worry about volt drop, however it is so easy to measure, the loop impedance tester will give us the volt drop with some calculations so radial 20 amp 0.79 Ω extra and with ring 0.59 Ω extra so a pedantic inspector can soon work out if exceeded. But today so few items have a problem with volt drop, fluorescent lamps with magnetic ballast, and fridge/freezers are about the only items today.

 

[Taylortwocities]

He does not live in the UK, and likely does not realise the problems with Part P.

what makes you say that?
In the OP he refers to a building notice, and LABC. So I don’t think he’s living in the Falklands?

 

[ericmark]

It say Melbourne, Australia.

 

[Taylortwocities]

Ah. I was referring to the OP.

 

[SUNRAY]

He does not live in the UK, and likely does not realise the problems with Part P.

And on that basis one may be excused for wondering if he is conversant with our electrical systems (seems to slag off our perfectly acceptable and standard ring final in favour of bulky, expensive and harder work radials). In which case it would not be unreasonable to wonder if he should be offering advice on here.

I have no idea of his experience/competence and therefore how valid his or my comments are.

 

[Dodgyrog]

..

 

[EFLImpudence]

Part P of The Building Regulations is a single sentence which states electrical work in dwellings must be carried out to ensure safety.

Nothing else.

 

[If in doubt...]

Hi,

Thanks for all the various replies. Apologies the deleted Dodgyrog reply above was from an old account of mine which Ive moved away from but accidentally logged in as - but purely as I started to think the jokey "Dodgy" bit might not be best when asking / giving advice.

So yes I am UK based and was saying that whilst competent in running T&E in to various sockets and keeping to the Horiz / Vert I am not fully Part P understanding and was hoping I could just run / extend off from one of those red star sockets. Want to keep final socket placement flexible as I build the room as still designing the layout as I go for wall mounted TV and light etc.

Father is retired / 20 years out of date LABC himself but his by the book advice is just deal with BC on black / white basis - ask YES / NO and if it is not legally required then BC does not need to know or get involved, but I am a bit more subtle / cooperative than that and he also understands that things may have changed, hence me wanting to understand more the background to what to expect.

So I guess my approach to BC is to say I intend to run those sockets / lights in that fashion, what do you need?

The actual detail as to whether I run vertically or horizontally etc I can look in to / check later.

 

[flameport]

So I guess my approach to BC is to say I intend to run those sockets / lights in that fashion, what do you need?

Yes.

No one here can know what BC will want in this specific situation.
Although extending existing circuits is not notifiable in itself, the electrical work is part of the whole extension, which is obviously notifiable.